CGI in Perl
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CGI
Programming
in Perl
Lecture 22 / Slide 2
CGI Programming
Last time we looked at designing a static web
page. Today we will see how to design dynamic
web pages using CGI programs.
A CGI program allows the user to interact with a
web page by generating HTML code that depends
on the user input.
For example, web pages with an entry form or
buttons use a CGI program to get the input from
the user, and display appropriate results.
Since the Web mainly contains text, Perl is the
most popular language for CGI programming
because it is good at text manipulation.
Lecture 22 / Slide 3
CGI Programming
cssystem considers CGI programs a security risk,
and does not allow them.
ITSC, however, allows CGI programs
– e.g., uststu1.ust.hk, uststu2.ust.hk
Place your CGI programs in a directory called
cgi-bin in your public_html directory.
mkdir $HOME/public_html/cgi-bin
Then, place your CGI programs under the directory
$HOME/public_html/cgi-bin and the URL is :
http://home-cgi.ust.hk/cgi-bin/cgiwrap/~login/program.cgi
Your CGI program should also have execute
permission set:
chmod a+x program.cgi
Lecture 22 / Slide 4
My ITSC Home Page
Lecture 22 / Slide 5
HTML of My Home Page
<HTML>
<HEAD><TITLE>Andrew Horner</TITLE></HEAD>
<BODY TEXT="aqua" LINK="violet" VLINK="deepviolet"
ALINK="green" BGCOLOR="black">
<P ALIGN=CENTER><B><font size="8" face="Arial">
Andrew Horner</font></B></P>
<P ALIGN=CENTER><B><font size="6" face="Arial">
<a href="http://www.cs.ust.hk/~horner">My "official" home
page</a></font></B></P>
<P ALIGN=CENTER><B><font size="6" face="Arial">
<a href="http://home-cgi.ust.hk/cgi-bin/cgiwrap/~horner/hello.cgi">
run CGI program</a></font></B></P>
</BODY>
</HTML>
Lecture 22 / Slide 6
Hello World CGI Program
Here is a “Hello World” CGI program:
#!/usr/local/bin/perl5 -w
# hello world CGI program
print <<END_OF_MULTILINE_TEXT;
Content-type: text/html
Blank line (no spaces or tabs) required!
<HTML>
<HEAD>
<TITLE>Hello World Program</TITLE>
</HEAD>
<BODY>
<H1>Hello World!</H1>
</BODY>
</HTML>
END_OF_MULTILINE_TEXT
Lecture 22 / Slide 7
Hello World Output
Lecture 22 / Slide 8
Here Documents
The previous example uses a here document.
It starts with the << and a word called the end
token (END_OF_MULTILINE_TEXT).
Here documents are a convenient way to quote
a multiline string.
The string begins on the next line and continues
up to a line containing the end token at the start
of the line.
Here documents are very useful for generating
HTML.
Lecture 22 / Slide 9
Hello World Details
The Content-type line identifies the type of
output we are generating (text/html).
It is immediately followed by a blank line, which
must contain no spaces or tabs. This line
separates the CGI header from the HTML code.
After the blank line comes the HTML, which is
sent to be formatted and displayed on the user’s
browser.
Lecture 22 / Slide 10
Testing CGI Programs
Make sure your program runs properly from the
command line before testing it on the web:
$ ~horner/public_html/cgi-bin/hello.cgi
Content-type: text/html
<HTML>
<HEAD>
<TITLE>Hello World Program</TITLE>
</HEAD>
<BODY>
<H1>Hello World!</H1>
</BODY>
</HTML>
$
Lecture 22 / Slide 11
The CGI Module
Using here documents in Perl is still a painful
way to generate HTML.
Perl has a CGI module to make it easier.
To use the CGI module in your program, include
the following line near the top of your program:
use CGI qw(:standard);
The use statement is like #include in C++; it
brings in predefined functions from another file
at compile time.
Lecture 22 / Slide 12
Simpler Hello World
Below is the “Hello World” program using the CGI
module:
#!/usr/local/bin/perl5 -w
# hello world CGI program using CGI module
use CGI qw(:standard);
print header();
print start_html("Hello World Program");
print h1("Hello World!");
print end_html();
CGI module functions return strings, which we can
then send to print.
Lecture 22 / Slide 13
Simpler Hello World
In the previous program,
header() returns a string containing the Contenttype line with a following blank line
start_html(string) returns string as an HTML title
h1(string) returns string as a first-level HTML
heading, and
p(string) would return string as a new HTML
paragraph.
Lecture 22 / Slide 14
Adding Textfields
CGI provides various widgets for accepting user input
in forms.
One of the most common widgets is the textfield
widget, which allows the user to enter text in a box.
In addition to start_html(), you also need
start_form() before you add your textfield.
textfield() is often called inside a p() function.
The first argument is the name of the textfield
The second argument is the default value.
print start_form;
print p("Bill is: ", textfield("bill","cheap"));
print end_form;
Lecture 22 / Slide 15
Hello Gates
A form with a textfield widget:
#!/usr/local/bin/perl5 -w
# Bill Gates CGI program
use CGI qw(:standard);
$billvalue = param("bill"); # get value from bill-field
print header(), start_html("Hello Bill Gates");
print h1("Hello Gates Lovers!");
if($billvalue){
# display, if user has hit Return
print p("Yes, Bill is $billvalue.");
}else{
# otherwise, ask for user-input
print hr, start_form; # hr() is <HR> HTML
print p("Bill is: ", textfield("bill","cheap"));
print end_form, hr;
}
print end_html();
Lecture 22 / Slide 16
Hello Gates Initial Screen
When we click on a link that points to this program,
you will see the below screen.
The text field is initially filled with the default value.
Lecture 22 / Slide 17
Hello Gates Result Screen
If the user does not change the default value, but
hits return, the following is displayed:
Lecture 22 / Slide 18
Hello Gates Screens
If the user changes the bill field as in the left
screen, the right screen results:
Lecture 22 / Slide 19
Other Form Widgets
Now we know how to create simple text fields and
respond to them.
What about other widgets like buttons, checkboxes,
and menus?
The program on the following slides includes:
popup menus,
a submit button (named “send”), and
a button to reset the entire form, erasing all user input.
Lecture 22 / Slide 20
Bill’s Fans page1
#!/usr/local/bin/perl5 -w
# Bill Gates CGI program v. 2
use strict;
use CGI qw(:standard);
print header(), start_html("Bill Gates Fans");
print h1("Bill Gates Fan Page");
if(param()){
# if the form has already been filled out
my $who = param("name");
my $what = param("billWord");
my $howmuch = param("money");
if($howmuch == 100){
print p("Yes $who, Bill is $what, and he has 100,000,000
times more money than you!");
}else{
print p("Incorrect $who! Bill has US\$100 billion.");
}
Lecture 22 / Slide 21
Bill’s Fans page2
}else{ # first time, so display clean form
print hr(), start_form();
print p("Your name: ", textfield("name"));
print p("What is Bill? ",
popup_menu("billWord", ["cheap", "rich", "powerful"]));
print p("How many billion US dollars does Bill have? ",
popup_menu("money", [1,10,100,1000]));
print p(submit("send"), reset("clear"));
print end_form;
}
print end_html();
Lecture 22 / Slide 22
References
Why the square brackets around the arrays in the
previous example?
["cheap", "rich", "powerful"]
[1,10,100,1000]
The brackets create a reference (pointer) to an array.
popup_menu() expects an array reference as its
second argument.
You can also create an array reference by using a
backslash in front of a named array, as in \@choices:
my @choices = qw(cheap, rich, powerful);
print p("What is Bill? ", popup_menu("billWord", \@choices));
Lecture 22 / Slide 23
Bill’s Fans Initial Screen
Here is the initial screen and default values the user
sees:
Lecture 22 / Slide 24
Bill’s Fans Initial Screen
The user fills in the form:
Lecture 22 / Slide 25
Bill’s Fans Result Screen
The resulting screen after the hitting “send”:
Lecture 22 / Slide 26
Bill’s Fans Result Screen
The resulting screen after the re-submitting the
correct value:
